title: A negative effector of blue light-induced and gravitropic bending in Arabidopsis.
abstract: Although sessile, plants are able to grow toward or away from an environmental stimulus. Important examples are stem or leaf orientation of higher plants in response to the direction of the incident light. The responsible photoreceptors belong to the phototropin photoreceptor family. Although the mode of phototropin action is quite well understood, much less is known of how the light signal is transformed into a bending response. Several lines of evidence indicate that a lateral auxin gradient is responsible for asymmetric cell elongation along the light gradient within the stem. However, some of the molecular key players leading to this asymmetric auxin distribution are, as yet, unidentified. Previously, it was shown that phototropin gets autophosphorylated upon illumination and binds to a scaffold protein termed NPH3 (for nonphototropic hypocotyl 3). Using a yeast three-hybrid approach with phototropin and NPH3 as a bait complex, we isolated a protein, termed EHB1 (for enhanced bending 1), with a so far unknown function, which binds to this binary complex. This novel interacting factor negatively affects hypocotyl bending under blue light conditions in Arabidopsis (Arabidopsis thaliana) and thus seems to be an important component regulating phototropism. Interestingly, it could be shown that the gravitropic response was also affected. Thus, it cannot be ruled out that this protein might also have a more general role in auxin-mediated bending toward an environmental stimulus.
authors.affiliation: Department of Plant Physiology, Justus-Liebig-University, 35390 Giessen, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Knauer
authors.forename: Michaela
authors.initials: M
authors.lastname: Dümmer
authors.forename: Frank
authors.initials: F
authors.lastname: Landgraf
authors.forename: Christoph
authors.initials: C
authors.lastname: Forreiter
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018522:Gravitropism / Q000502:physiology*; D018546:Hypocotyl / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D056949:Phototropins / Q000378:metabolism; D018524:Phototropism / Q000502:physiology*; D010937:Plant Growth Regulators / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; C000597452:EHB1 protein, Arabidopsis; D007210:Indoleacetic Acids; C400222:NPH3 protein, Arabidopsis; D056949:Phototropins; D010937:Plant Growth Regulators